I call one male friend Oppa...and I may have slipped and called my mom Omma once. I also sang her the 3 Bears nursery rhyme. I do utter "aish" a lot...it saves me from saying a curse word in certain situations. Sometimes I respond with Ani or Ne. Oh, sometimes I tell a friend "Fighting," she'll say it to me (like during my exams), or I'll say it to myself. For me, it's always accompanied by the fist pump, and my pronunciation is more "Hwaiting." I even wrote the term (in Hangul) on my golf balls >_< lol. More terms find their way into my vocabulary like jinjja, gurae(yo), ottoke, omo, wae, nawa, gaja...
Other than language, however, I've picked up some mannerisms. I watch a LOT of Korean variety shows, and I've picked up on the girlish laugh clap and the hand(s) over the mouth while laughing thing. I've also kind of picked up on bowing or nodding as someone else mentioned. Thankfully, I don't 90º bow, but I'll do a slight dip with my head and shoulders sometimes.